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Apache Kafka

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Table of Contents

Quality: Silver Tier.

🐙 userver provides access to Apache Kafka Brokers via two independent interfaces: kafka::ProducerComponent and kafka::ConsumerComponent.

They expose APIs for sending messages to Kafka topics, suspending coroutine until message delivery succeeded or failed, and for process message batches from the subscribed set of topics, asynchronously polling messages in separate task processor.

Common Features

  • Easy to configure (compared with raw Kafka clients with dozens of options);
  • No message payload copying;
  • Support of SASL SCRAM-SHA-512 authentication and SSL transport for Broker communication;
  • Comprehensive logs of all events and errors;
  • Metrics;
  • Kafka message headers support;

Producer Features

  • 🚀 Parallel cooperative messages delivery reports processing (in comparison with all librdkafka-based Kafka clients, the performance of which rests on a single thread);
  • 🚀 No blocking waits in implementation (message senders suspend their coroutines execution until delivery reports occurred);
  • Synchronous and asynchronous non-blocking interfaces for producing messages;
  • Automatic retries of transient errors;
  • Support of idempotent producer (exactly-once semantics);
  • Sending message to concrete topic's partition;

Consumer Features

  • 🚀 No blocking waits in implementation (message poller suspends the coroutine until new events occurred);
  • Callback interface for handling message batches polled from subscribed topics;
  • Balanced consumer groups support;
  • Automatic rollback to last committed message when batch processing failed;
  • Partition offsets asynchronous commit;

Metrics

Producer and consumer yields same set of metrics (but with different prefixes):

Metric name Labels Description
kafka_producer.avg_ms_spent_time component-name, topic Average message producer latency
kafka_producer.messages_total component-name, topic Total number of sent messages
kafka_producer.messages_success component-name, topic Number of messages successfully written to partition
kafka_producer.messages_error component-name, topic Number of messages failed to produce
kafka_producer.connections_error component-name Number of broker connection errors occurred
kafka_consumer.avg_ms_spent_time component-name, topic Average time between message written to partition and read by consumer
kafka_consumer.messages_total component-name, topic Total number of read messages
kafka_consumer.messages_success component-name, topic Number of successfully processed messages
kafka_consumer.messages_error component-name, topic Number of messages user-callback failed
kafka_consumer.connections_error component-name Number of broker connection errors occurred

See Service Statistics and Metrics (Prometheus/Graphite/...) for info on how to get the metrics.

Planned Enhancements

  • ✅ Transfer from raw polling with timeouts to events processing, making the message polling non-blocking and leading to better library scalability;
  • ✅ testsuite Kafka support in OSS;
  • Support of different compression codecs (GZIP, LZ4, ZSTD, etc..);
  • Support more SASL authentication mechanisms (GSSAPI, OAUTHBEARER);

Unit and functional testing

  • Kafka service shows how to test userver services with Kafka consumers and producers;
  • kafka::utest::KafkaCluster may be used for convenient unit testing with local consumers and producers instances;

More information